This application is based on Application No. 2002-26172 filed in Japan on, Feb. 1, 2002, the content of which is incorporated hereinto by reference.
The present invention relates to a method and a device for detecting a current with accuracy, and especially relates to a method and a device for detecting a current adequately in a rechargeable battery on-board of a hybrid car with accuracy.
An electric vehicle such as hybrid car, and so on, calculates the rest of the capacity of the rechargeable battery, which drives a motor for driving, with integrating the current of charging and discharging. At this time, it is very important to detect the current with accuracy, and to calculate the rest of the capacity of the rechargeable battery certainly. The reason is that the error of calculation of the rest of the capacity at calculating the current affects the life of the rechargeable battery, and further affects the driving condition. Because charging and discharging are controlled based on the rest of the capacity, if the rest of the capacity calculated with the current is not accurate, over-charging or over-discharging the rechargeable battery may deteriorate its characteristics. In addition, because the driving condition is controlled based on the rest of the capacity, the driving condition may also be deteriorated, for example the acceleration is getting poor. Especially in the rechargeable battery for a vehicle, charging and discharging are controlled to keep around 50% of the rest of the capacity, so as to maximize prolongation of the life. Using in this condition can minimize reduction of the battery performance. However, because charging and discharging the rechargeable battery in this range do not achieve full-charge or complete-discharge, it is difficult to correct the rest of the capacity. The reason is that the rest of the capacity should be corrected with full-charge or complete discharge in the battery. When the rest of the capacity is calculated with integrating the current of charging and discharging for a long time without correcting the rest of the capacity, the cumulated errors may be getting inaccuracy according to cumulating them, even each error is small. So that it is important to maximize the accuracy of detecting the current in charging and discharging.
There are two types of conventional current-detecting devices. One is a type detecting a current with magnetic changes by a magnetic current sensor; another is a type detecting an integrated value during a predetermined time period with detecting voltage between both ends of a current-detecting resister. The type with the magnetic current sensor has the advantage that the current can be detected in high rate with predetermined sampling period. However, it is difficult to detect a current with accuracy in a large current range. Especially, it is tend to occur the error, when a large current is detected. In addition, in this type, the error of the detection can be also occurred cause of the influence of the remanence of the sensor itself. Thus, it is difficult to detect the current with accuracy in a large current range in this type. On the other hand, the type cumulating the voltage of the current-detecting resister has the advantage that the current can be detected with high accuracy. However, there is a detecting-incapable time period, which is incapable of detecting a current, for example the timing to communicate about the calculated current. Thus, the current cannot be detected in all time period with high accuracy. Especially, the error should be increased when the current changes in the detecting-incapable time period, so that it has the disadvantage that the current changing sharply cannot be detected with accuracy.
The invention was developed with the aim of eliminating these drawbacks. An important object of the invention is therefore to provide to a method and a device for detecting a current with high accuracy, even if the current changes sharply.
In the method for detecting a current of the invention, the current is detected by a first current sensor with a predetermined sampling period as a digital value, and is detected by a second current sensor with high accuracy with a period longer than the first current sensor as a digital value. Further, the current during detecting-incapable time period, which is incapable of detecting the current between detecting timings for detecting the current in the predetermined period by the second current sensor, is complemented with the current value detected by the first current sensor.
In the method for detecting a current of the invention, the current can be detected by the first current sensor and the second current sensor asynchronously. In this method for detecting the current of the invention, a detecting time period detecting the current by the second current sensor is calculated with comparing the detected current of the second current sensor with the detected current of the first current sensor, the detecting-incapable time period is specified based on the calculated detecting time period, and the current during the detecting-incapable time period is complemented with the detected current of the first current sensor.
The device for detecting a current includes a first current sensor detecting the current with predetermined sampling period, and a second current sensor detecting the current with high accuracy with a period longer than the first current sensor. In the device, the second current sensor detects the current with the predetermined period, and the current during a detecting-incapable time period, which is incapable of detecting the current by the second current sensors, is complemented with the current value detected by the first current sensor.
The device for detecting a current further includes a calculating circuit calculating the current value based on the detected currents of the first current sensor and the second current sensor, and the first current sensor and the second current sensor can detect the current asynchronously. The calculating circuit calculates a detecting time period detecting the current by the second current sensor with comparing the detected current of the second current sensor with the detected current of the first current sensor, specifies the detecting-incapable time period based on the calculated detecting time period, and complements the current during the detecting-incapable time period with the detected current of the first current sensor.
The method and the device for detecting a current mentioned above have the advantage that the current can be detected with high accuracy, even if the current changes sharply. The reason is that combining the first current sensor detecting the current with predetermined sampling period and the second current sensor detecting the current with high accuracy with a period longer than the first current sensor can complement the current during detecting-incapable time period, which is incapable of detecting the current by the second current sensor, with the current value detected by the first current sensor. Further, the method and the device mentioned above complement the current during the detecting-incapable time period in the second current sensor, which can detect a current with high accuracy but cannot detect all the time period, with the current value detected by the first current sensor. Thus, the advantages of both sensors can obtain the higher accurate current value than each sensor alone.
Furthermore, in the invention, even if the second current sensor does not work temporarily, or the data cannot be read cause of noise or the like, the first current sensor can complement with detecting the current value. Therefore, the accurate current value can be detected all the time, and it is advantageous to achieve high reliability.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.